356 READINGS IN BIOLOGICAL SCIENCE 



German, Anton de Bary, stared at the dying potato leaves through his 

 primitive microscope, saw the green leaf cells in the clutches of the sinuous, 

 pallid fibers of the fungus, and its myriads of wind-driven spores, proved 

 that the fungus was the cause, the sole cause of the blight, and paved the 

 way for Alillardet a few years later to give humanity an effective weapon 

 against any future recurrence of the blight, Bordeaux mixture. 



The story of Bordeaux mixture itself is worth the telling. According 

 to the tale, a farmer in Medoc, France, had a vineyard that bordered the 

 highway. Passers-by are alike the world over, and to the despair of the 

 farmer, the wayfarers could not resist the luscious bunches of ripening 

 grapes, just over the fence. In a moment of inspiration, the farmer decided 

 to take steps. He went to the barn, and his eye falHng on a sack of lime, 

 he made a milky broth to splash on the vines. As the mixture didn't look 

 repulsive enough, he threw in a shovelful of bluestone. This accomplished, 

 he spattered it over the vines, posted a "Poison" sign and awaited results. 

 History does not tell us whether the wayfarers were deterred by the 

 farmer's ingenuity, but it does recall that Dr. Millardet came past the vine- 

 yard, noted that the sprayed grapes alone had escaped the destructive 

 mildew disease, learned of the spray so accidentally appHed, tested its ef- 

 ficiency against fungus diseases of the vine, and gave us the completely ef- 

 fective protection against future outbreaks of both vine and potato blights 

 which we now know as Bordeaux mixture. 



Man has a tendency to learn things the hard way. It took another epiphy- 

 totic which has practically exterminated one of our finest forest trees, the 

 American chestnut, to establish the science of plant pathology in America. 

 The chestnut blight fungus was a foreigner that sneaked into America from 

 Asia. Starting its deadly work about 1904, it spread swiftly, destroying 

 every tree in its path. Today there hardly remains a chestnut tree in the 

 great forests of the East which were once dominated by this tree. This 

 disaster taught us what might be expected from unwelcome foreign pests; 

 it was largely responsible for the establishment of the National Plant 

 Quarantine Act in 191 2. 



Today new and potent enemies of our cultivated plants are coming to 

 the attention of growers and scientists. The Dutch elm disease for a while 

 threatened to exterminate the American elm, as it had done in many parts 

 of Europe. In the royal gardens at Versailles were long avenues of stately 

 elms that were mature trees in the hey-day of the pre-revolution French 

 court. Only a few years after the Dutch elm disease appeared, the avenues 

 were Kned with dead and dying trees, nearly all sacrificed to the elm disease 

 fungus. Thanks to our lesson from the chestnut blight and to energetic 

 eradication of diseased elms in America, the elm disease has been brought 

 under control, but any relaxation of these efforts could still release the 

 disease in all its destructiveness. 



Few of the main groups of crop plants are free from occasional but 



